Three-phase transformer cores



2 Shets-Sheet 1 Filed Nov. 15, 1950 Fuel.

J. CHARLES JOUBLANG INVEN THREE PHAsE TRANSFORMER CORES Filed Nov. 13, 1950 2 Sheets-Sheet 2 FIGZ.

J. CHARLES JOUB C INVENW A ORNEY United States Patent THREE-PHASE TRANSFORMER CORES Joseph Charles Joublanc, Zanesville, Ohio, assignor to McGraw Electric Company, Milwaukee, Wis., a corporation of Delaware Application November 13, 1950, Serial No. 195,238

2 Claims. (Cl. 336-5) This invention relates to three-phase transformers, and is particularly directed to the core construction and arrangement.

For many years transformers were made of stacked core construction, in which a multitude of pieces of fiat core steel were joined together by stacking, to form the necessary shape of core. This method was costly and time consuming.

To overcome these difliculties, a simpler method of stacking of magnetic ribbons was introduced. Progressively shorter lengths of magnetic ribbons were stacked and bent upwardly to form the desired core shape. The ends were either abutted against one another or interleaved. The final core was held together in some manner and annealed to retain the core shape. After annealing, the core was opened and a conducting winding assembly slipped over the free end. The interleaved or abutted ends were then held together with a band or with a non-conducting clamp, or the like.

The next improvement in core structures was the introduction of closed cores of wound magnetic ribbons. These round-wound cores were formed rapidly and with simple tools. The magnetic ribbon used in winding the cores is produced by a rolling process. As indicated above, another great advantage of magnetic cores of the wound type is that the strip of magnetic material forming the core may be easily arranged so that the path of the magnetic flux and all parts of the core will follow the direction in which the strip is rolled. A three-phase transformer using a core structure of this type is disclosed in the U. S. Pat. No. 2,401,952, granted to Walter R. Mayberry on June 11, 1946, and assigned to the same assignee as the present invention. After the cores were wound, the conducting winding assembly was wound in any suitable manner as by means of a winding machine of the type shown in the Steinmayer et al. Patent No. 2,305,999 of December 22, 1942, also assigned to the same assignee as the present invention.

The primary object of this invention is to provide a novel form of a three-phase transformer which has as its core structure three closed cores, each preferably composed of a plurality of layers or sections of different widths, and which are arranged to provide a core structure supporting three conducting winding assemblies in such manner as to require a minimum of mounting space. In addition, the novel structure requires a minimum of supporting hardware effecting a substantial reduction in cost of the transformer.

Further objects are to provide a three-phase transformer which has three identical, triangularly wound cores with the triangular cores positioned adjacent one another to form a larger triangularly shaped structure or assembly with each of the three conducting winding assemblies including the primaries and secondaries surrounding adjacent straight leg portions of two cores. This has been found to produce an economical design of a three-phase transformer permitting a relatively smaller transformer tank.

Further objects are to provide a wound core construction for a three-phase transformer in which the three cores forming the three core units of the transformer lie in approximately the same plane, thus simplifying the tank construction and allowing the mounting of the transformer in a roughly rectangularly shaped, vertically arranged tank, if so desired.

Further objects are to provide a wound core construction for a three-phase transformer, in which the three 2,702,887 Patented Feb. 22, 1955 core units of the transformer lie in approximately the same plane, permitting two of the conducting windings to be located in the lower portion of the transformer tank which has the cooler oil circulating about the windings and with only one winding in the upper portion of the tank where the hotter oil is circulated. Thus, the heat emanating from the conducting windings will be evenly distributed to the oil, therefore providing greater dissipation of heat from the tank surface.

Embodiments of the invention are shown in the accompanying drawings, in which:

Figure 1 is an elevation of the transformer with parts token away and parts in section.

Figure 2 is a cross-sectional view of the transformer taken on line 22 of Figure 1.

Figure 3 is a reduced elevational view of another em bodiment of this invention.

Figure 4 is a view, partly in section, of a method of clangping the cores of the embodiment disclosed in Figure Referring to the drawings, it will be seen that a preferred type of three-phase transformer is shown in Figure 1, and is provided with three cores generally indicated at A, B, and C. These cores are identical and a description of one will therefore suffice. Each core is preferably formed by winding a closed core of magnetic ribbon on a triangularly shaped mandrel. The material used in making the cores is any suitable type of magnetic ribbon, though it is preferable to use silicon steel which may be either hot rolled or cold rolled, as this material has been found highly efiicient in the manufacture of transformers.

Referring now to Figure 2, the cores are preferably wound in step-fashion. Thus, cores positioned adjacent one another will provide a cruciform cross-section as shown. The wound layers, or sections, 1, 2, 3, and 4 are wound of progressively wider ribbons, and any number of sections can be used.

The triangular shaped cores are placed adjacent one another as is shown in Figure 1, the combination of the three cores forming a larger triangular shaped structure or assembly. As suggested above, these core sections are preferably wound on triangularly shaped mandrels. The invention is not limited in its broadest aspect to a closed, wound core construction and a further form of the invention will be described hereinafter. However, after the cores have been completely wound or formed, they are annealed While clamped in their finished shape. The completely wound cores are not thereafter worked at all by bending or by any other means and the cores, as formed in the manner hereinafter described, are worked a minimum amount. Lesser working of the cores produces a substantially lower internal strain in the core, which in turn produces minimum electrical power losses.

Conducting winding assemblies, indicated by the reference characters 5, 6, and 7, are wound in place around adjacent legs of each of two core sections, as shown most clearly in Figure 1. These conducting winding assemblies, including both primary and secondary coils, may be wound in any suitable manner, for example as shown in the Steinmayer et a1. patent.

The conducting winding assemblies 5, 6, and 7 are preferably round-wound to thereby secure all of the advantages inherent in round-wound conducting assemblies which resist distorting forces due to short circuiting or similar conditions better than rectangular preformed coils as the circular coil is considerably stronger than the rectangular coil. In addition to the above enumerated advantages, the winding of circular conducting winding assemblies entails less danger of damage to the insulation during winding and where a rectangular conducting winding assembly requires less tension on the wire during winding and requires no pounding of the coil to make a firm coil.

As stated above, the cores A, B, and C are wound in step-fashion, as is clearly shown in Figure 2. It will be obvious that when two cores, such as A and B, are placed with legs adjacent one another, the two legs will provide a cruciform cross-section that will nearly completely fill the window of the conducting winding assembly 5 as is shown in Figure 2. Thus, an excellent space factor is provided. Obviously, a single width ribbon could be used throughout, though the stepped form is preferred.

After the winding assemblies have been completed, any suitable type of wedges may be employed to prevent shifting of the conducting winding assemblies. For example, wedges indicated by the reference characters 8, 9, and 10 may be positioned as is shown in Figure 1. The wedges may be made of wood blocks, plastic, or any other suitable insulating material.

It will be apparent that it is within the scope of this invention to provide a modified core structure as is clearly shown in Figure 3. This modification incorporates the use of a stacked core assembly. Magnetic ribbon is sheared and preferably cut to progressively smaller lengths and widths. These pieces are stacked on one another and the stack is bent upwardly to form a triangular shaped structure with open ends. The ends are either interleaved as shown, or brought into abutted relationship under well-known practice. The cores A, B, and C' are each clamped in this shape and annealed to relieve working stresses. After annealing, the ends are brought apart, but not beyond the elastic limit of the material.

Each of the triangular cores is preferably slipped through previously wound conducting assemblies 5', 6', and 7' to provide the triangular structure or assembly shown in Figure 3. Again, this modification preferably provides a cruciform cross-section between adjacent legs substantially as indicated in Figure 2 to substantially fill the window of the conducting assembly and thus pro vide an excellent space factor. Obviously, the stacked pieces could be of the same width, though the stepped form is preferred. It will also be apparent that the cores may be cut and interleaved in more than one place without departing from the scope of this invention.

The ends of the stacked core laminations of each core of this modified core structure or assembly may then be interleaved as shown in Figure 3 and clamped together. A simple clamp, indicated generally by the reference character 11, may be provided as shown in Figure 4. A U-shaped band 12 is formed to closely surround the stacked and interleaved laminations and is insulated therefrom by a strip of insulating material such as pressboard 13. The free ends are brought in clamping relationship with a rivet or bolt and nut assembly 14 which is insulated from the band 12 by flanged insulating sleeves 15.

Suitable wedges may be employed to prevent shifting of the conducting winding assemblies. The wedges may be made of wood blocks, plastic, or any other suitable insulating material, and are indicated in Figure 3 by reference characters 8, 9', and 10'.

It will be seen that a three-phase transformer has been provided in which the three conducting winding assemblies are arranged to lie in a single plane forming a novel triangular shaped structure or assembly, that will provide a most economically designed transformer, which structure may be placed in a compact and relatively small transformer tank.

Each winding assembly surrounds or interlinks two adjacent cores and the magnetic flux does not at any time have to pass from one core to another core. It will be apparent that the structure may be modified in any desired manner, retaining radially disposed conductive windings arranged in substantially the same plane and still remain within the scope of this invention, as defined by the appended claims.

Having now particularly described and ascertained the nature of this invention and in what manner the same is to be performed, I declare that What I claim is:

1. A three phase transformer of general triangular configuration including three separate and distinct contiguous substantially triangular closed core sections of substantially the same size lying substantially in a coInmon plane, said sections each having two winding leg portions each of which is juxtaposed respectively to a winding leg portion of an adjacent section, said juxtaposed portions jointly providing a winding leg, each section being of lengthwise bent, concentrically nested laminations of magnetic sheet material disposed in planes substantially perpendicular to said common plane, and an electrical winding assembly on each winding leg includ ing a primary winding portion and a secondary winding portion both of which surround said juxtaposed leg portions in embracing relationship, said winding assemblies being adapted to be connected to different phases of a three phase electrical system.

2. A three phase transformer of general triangular configuration including three separate and distinct contiguous substantially triangular closed core sections of substantially the same size lying substantially in a common plane, said sections each having two winding leg portions each of which is juxtaposed respectively to a winding portion of an adjacent section, each section being of lengthwise bent, concentrically stacked laminations of magnetic strip material of different widths disposed in planes substantially perpendicular to said common plane with the narrowest strip disposed interiorly and the widest strip disposed exteriorly to provide a stepped cross section, said juxtaposed portions jointly providing a Winding leg of cruciform cross section, and an electrical winding assembly on each winding leg including a primary winding portion and a secondary winding portion both of which are circumjacent said juxtaposed leg portions in embracing relationship, said winding assemblies being adapted to be connected to different phases of a three phase electrical system.

References Cited in the file of this patent UNITED STATES PATENTS 400,862 Lowrie et al. Apr. 2, 1889 422,746 Dolivo-Dobrowolsky Mar. 4, 1890 564,944 Sessions July 28, 1896 1,933,140 Gakle Jan. 29, 1929 2,344,294 Evans Mar. 14, 1944 2,400,184 Woolfolk May 14, 1946 2,401,952 Mayberry June 11, 1946 2,431,128 Link Nov. 18, 1947 2,616,070 Corbino Oct. 28, 1952 FOREIGN PATENTS 583,957 Great Britain Jan. 3, 1947 

